Polymerization Kinetics-Mediated Topological Entanglement Enables High-Contrast 3D Self-Morphing in Hydrogels.

Creating anisotropic networks with spatially programmed, pronounced swelling gradients to advance the morphological complexity and functionality of self-morphing hydrogels is crucial, yet remains a formidable challenge. Here, we present a polymerization kinetics-mediated strategy to spatially modulate both topological entanglement and interchain interactions, generating localized domains with vastly different swelling ratios for high-contrast 3D shape transformation. This approach leverages the kinetic competition between chain growth and mass transport during polymerization. Unlike rapid polymerization, slow polymerization allows substantial inward diffusion of unreacted monomers and formation of interpenetrating polymer networks, resulting in densely entangled chain architectures across multiple polymerization stages. Critically, such entanglements not only act as physical crosslinks but also enhance interchain hydrogen bonding, weakening polymer-water interactions and reducing osmotic pressure. By introducing hydrogen-bonding or polyelectrolyte effects, we significantly amplify differences in interchain interactions and equilibrium swelling ratio between rapidly and slowly polymerized hydrogels. Consequently, by spatially modulating ultraviolet light intensity, a pronounced disparity in entanglement density and interchain interactions is achieved between adjacent regions, yielding a striking 23-fold difference in swelling ratio. This sharp local swelling contrast enables intricate, high-cavity 3D morphologies unattainable with conventional self-morphing hydrogels, broadening the architectural versatility and application potential of hydrogel-based adaptive materials.